The present technique relates to a vehicle drive including power electronic devices and their incorporation into modules and systems. More particularly, the technique relates to the configuration, packaging and thermal matching within of power electronic devices in such devices.
A wide array of vehicle drives are known including power electronic devices, such as power switches, transistors, and the like. For example, silicon controlled rectifiers (SCRs), insulated gate bipolar transistors (IGBTs), field effect transistors (FETs), and so forth are used to provide power to loads. In certain applications, for example, arrays of power switches are employed to convert direct current power to alternating current waveforms for application to loads, typically an electric vehicle motor.
In electric vehicles, a source of direct current is typically available from a battery or power supply system incorporating a battery or other direct or rotating energy converter. Power electronic devices are employed to convert this power to alternating current waveforms for driving one or more electric motors. The motors serve to drive power transmission elements to propel the vehicle. While numerous constraints exist in such settings which differ from those of industrial settings, numerous problems and difficulties are shared in all such applications.
Demands made on power electronic devices typically include their reliability, power output, size and weight limits, and requirements regarding the environmental conditions under which they must operate. Where size and weight constraints force reductions in the packaging dimensions, difficulties arise in appropriately placing the power electronic devices, and drive and control circuitry associated with the devices to sufficiently remove heat generated during their operation. Where size, cost and weight are less important, large heat sinks and heat dissipation devices may be employed utilizing any fluid that can be accommodated by choice of materials that are compatible. However, as packaging sizes are reduced, more efficient and effective techniques are needed. Electrical and electronic constraints also impose difficulties on package design. For example, reduction of inductance in the circuits and circuit layout is commonly a goal, while solutions for reducing inductance may be difficult to realize. Shielding from electromagnetic interference originating both within the package and outside the package may be important, depending upon the surrounding environment. Similarly, appropriate interfacing with external circuitry, and the facility to install, service and replace power electronics packages may be important in certain applications. It has typically been necessary in many instances to configure the power electronic element to match closely the specific needs of the application and by doing so meet cost, size, performance targets that can be achieved by no other means. Finally, certain environments, such as vehicle environments, impose a wide range of difficult operating conditions, including large temperature spans, vibration and shock loading, and so forth.
A particular problem arising in power electronics circuitry, and particularly in converting circuitry arises from differential thermal expansion and contraction between various circuit components. Because extremes in environmental and enclosure temperatures, significantly different rates of expansion and contraction may arise within the power electronics circuits and within supporting structures. In such circumstances, delamination, deterioration, and malfunction can arise due to repeated thermal cycles and the consequent expansion and contraction. A particular challenge arises in cooling such circuitry, while preventing the degradation of the packaging and circuitry due to the thermal expansion and contraction.
There is a need, therefore, for improved techniques in packaging of power electronic devices in vehicle drives. There is a particular need for techniques which offer good thermal management while addressing the issue of differential thermal expansion and contraction.